In order to create a more immersive audio experience, upmixing processes can be applied to the audio signals to create additional surround channels from the original audio signals, for example, from stereo to surround 5.1 or from surround 5.1 to surround 7.1, and the like. There are many upmixers and upmixing algorithms. In those conventional upmixing algorithms, the created additional surround channels are generally for floor speakers. In order to further improve the spatial immersive experience, some upmixing algorithms have been proposed to upmix the audio signals to height (overhead) speakers, such as from surround 5.1 to surround 7.1.2, where the “0.2” refers to the number of height speakers.
The conventional upmixing solutions usually only upmix the diffuse or ambiance signals in the original audio signal to the height speakers, leaving the direct signals in the floor speakers. However, some direct signals, such as the sounds of raining, thunder, helicopter or bird chirps, are natural overhead sounds. As a result, the conventional upmixing solutions sometimes cannot create a strong enough spatial immersive audio experience, or even cause some audible artifact in the upmixed signals.